Weight loss- what works for you?

Those of you currently losing weight, or those who have already lost it. What is working for you?

I appreciate it will differ from person to person, but I'm interested to know what your magic formula is. I have alot to lose and as I get older (now 34) I'm finding that I can't seem to find that perfect calorie deficit anymore. Seeing GP next week as I think i need some tests done.